1. Field of the Invention
The present invention relates to an exposure apparatus, a device manufacturing method, and an aperture stop manufacturing method.
2. Description of the Related Art
There is conventionally known a projection exposure apparatus that illuminates a mask via an illumination optical system including an optical integrator configured to make uniform illumination light, and exposes a pattern of the mask onto a substrate via a projection optical system. An improvement of a resolution has recently been increasingly required for the projection exposure apparatus.
An off-axis illumination, such as a dipole illumination or a quadrupole illumination, is effective to the improvement of the resolution, and an off-axis illumination having a predetermined effective light source shape can be realized by an aperture stop arranged on an exit surface of the optical integrator (or a pupil in the illumination optical system). In particular, recently, an oblique incidence illumination is often required which uses an aperture stop that is very short in its radial direction. See Japanese Patent Laid-Open Nos. 2007-080947 and 5-315226.
The aperture stop is arranged at a (defocus) position that shifts from a back focal plane of the optical integrator so as to avoid the mechanical interference. This configuration causes a difference of an effective light source distribution for each image height on a surface to be illuminated, and an asymmetrical effective light source distribution at the off-axis position on the surface to be illuminated. As a result, critical dimension (“CD”) variations of a pattern formed on the substrate increase, and the yield deteriorates. In particular, this influence cannot become ignored in the extremely oblique incidence illumination (having a large incident angle) which is recently required.